To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post LTE system’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like.
In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
In the recent years several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and to provide more and better applications and services. The 3rd Generation Partnership Project 2 (3GPP2) developed Code Division Multiple Access 2000 (CDMA 2000), 1× Evolution Data Optimized (1× EVDO) and Ultra Mobile Broadband (UMB) systems. The 3rd Generation Partnership Project (3GPP) developed Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) and Long Term Evolution (LTE) systems. The Institute of Electrical and Electronics Engineers developed Mobile Worldwide Interoperability for Microwave Access (WiMAX) systems. As more and more people become users of mobile communication systems and more and more services are provided over these systems, there is an increasing need for an advanced wireless communication system with large capacity, high throughput and lower latency.
One of the key goals for the advanced wireless communication system is to support peak data rate of the order of 50 Giga bits per second (Gbps) and an average user throughput of the order of 1 Gbps. The implementation of latest wireless communication technologies like LTE, Advanced WiMAX in the mobile handsets currently supports protocol stack medium access (MAC) layer throughput up to 100 mega bits per second(Mbps). Supporting very high data rate of the order of Gbps is a challenge in the mobile handsets. The tremendous increase in throughput from 100 Mbps to 50 Gbps impacts one or more of the following parameters:    a) Number (N) of MAC Protocol Data Unit (PDUs) to be Processed: The MAC layer in protocol stack provides MAC Protocol Data Unit (PDU) to Physical layer for transmitting in one physical burst. One physical burst may carry one or more MAC PDUs. The increase in throughput will lead to increase in number of MAC PDUs to be processed in a given time. If the packet size and the transmit time interval (TTI) in which one packet is transmitted is same in current wireless communication technology and the advanced wireless communication technology then the number of MAC PDUs that needs to be processed in advanced wireless communication technology is 500 times more than the number of MAC PDUs processed in current wireless communication technology. If the transmit time interval is reduced by 10 times in advanced wireless communication technology then also 50 times more MAC PDUs needs to be processed in 1/10 of the time in advanced wireless communication technology.
The only way to keep the number of MAC PDUs to be processed in advanced wireless communication technology same as the number of MAC PDUs processed in current wireless communication technology is to increase the packet size by 500 times which is practically not possible. The table 1 below lists various combinations of TTIs, packet sizes and number of MAC PDUs required to be processed in advanced wireless communication technology.
The table 1 is Number of MAC PDUs to be processed in advanced wireless communication technology.
TABLE 1PacketPacketNTTIAdvancedTTICurrentSizeAdvancedSizeCurrent500x  1 ms1 ms12500 bytes10 mb/1 s = 12500bytes phy burst per1 ms TTI50x0.1 ms1 ms12500 bytes12500 bytes50x 1 ms1 ms12500 bytes12500 bytes 5x0.1 ms1 ms12500 bytes12500 bytes    b) Time Interval in which (N) MAC PDUs are Transmitted and Received in the Transmitter and Receiver Respectively: The transmit time interval in the advanced wireless communication technology is likely to be smaller than the current wireless communication technology. For example, if higher frequency (example mmWave frequency) spectrum is used in advanced wireless communication technology then the transmit time interval is going to be smaller because of the mmWave channel characteristics. The reduced transmit time interval will also assist in reducing the user plane latency in advanced wireless communication technology.    c) Packet Size: The packet size in the advanced wireless communication technology may be kept same or larger than the current wireless communication technology.
Based on the above illustration, it can be inferred that in the advanced wireless communication technology more number of packets, larger in size needs to be processed in shorter time.
The implementation of latest wireless communication technologies like LTE, Advanced WiMAX in the mobile handsets currently supports protocol stack medium access (MAC) layer throughput up to 100 mega bits per second(Mbps). In current systems (esp. on mobile station side), generally, one central processing unit (CPU) is used and most of the operations have to be scheduled on this CPU in a serialized manner. The CPU in the current implementation is already fully loaded for processing the supported data rates. One way to further improve the supported data rates is by increasing the CPU clock speed. However, increasing the CPU clock speed has its limitations in terms of power consumption and heat dissipation among other issues.
The user plane architecture in the current wireless communication technology (e.g. LTE) as illustrated in FIG. 1 comprises of user equipment (UE) 101, enhanced node B (eNB) or base station 102, serving gateway 103 and packet data node (PDN) gateway 104. Evolved Packet Service (EPS) bearer is established between the UE 101 and PDN gateway 104 for the transportation of application packet (or internet protocol (IP) packet). EPS bearer is a bearer corresponding to an IP packet flow with a defined QoS between the UE 101 and PDN gateway 104. EPS bearer may be bidirectional or unidirectional. Multiple bearers can be established for an UE 101 in order to provide different QoS streams or connectivity to different PDNs 104. For example, a user might be engaged in a voice (VoIP) call while at the same time performing web browsing or File Transfer Protocol (FTP) download. A VoIP bearer would provide the necessary QoS for the voice call, while a best-effort bearer would be suitable for the web browsing or FTP session. S5/S8 bearer transports the packet of an EPS bearer between the PDN gateway 104 and serving gateway 103. S1 bearer transports the packet of an EPS bearer between a serving gateway 103 and eNB 102. S-GW 103 stores a one-to-one mapping between an S1 bearer and an S5/S8 bearer. The bearer is identified by the GTP tunnel ID across both interfaces. A radio bearer (RB) transports the packets of an EPS bearer between an UE 101 & an eNodeB 102. There is one to one mapping between the EPS bearer, RB, S1 bearer and S5/S8 bearers.
FIG. 2 illustrates the mapping of application or IP flows, EPS bearer/Radio bearer in the current wireless communication technology (e.g. LTE). Applications or IP flows having different QoS are mapped to different EPS bearer. For example application 1 & application 2 are mapped to EPS bearer 1 and EPS bearer 2 respectively. Applications/or IP flows are mapped to EPS bearer based on packet classification rule or transmit flow template i.e. source IP address, destination IP address and port number of IP flow. Applications having same QoS can be mapped to same EPS bearer. For example, application 4 & application 5 are mapped to same EPS bearer 5. Application having different type of packets (e.g. control, data) can be mapped to multiple EPS bearers. For example application 3 is mapped to EPS bearer 3 and EPS bearer 4. EPS bearer 3 carries control packets of application 3 whereas EPS bearer 4 carries data packets of application 3. There is one to one mapping between EPS bearer & Radio bearer. A radio bearer exists for every EPS bearer.
Each packet in the user plane is processed by functions defined by various layers. The packet processing functions through which each packet of an IP flow goes through in the transmitter and receiver is illustrated in FIG. 3.
Process performed at transmitter 300A:
At step 301, IP packets (received from an application/IP layer in case of UE and serving gateway in case of eNB) are mapped to one or more radio bearers. At step 302, the IP packets are sequenced according to a packet number. At steps 303 and 304, the header compression & security functions are performed. At step 305, ARQ process is performed which includes generation of ARQ block and process of ARQ window. Here ARQ means Automatic Repeat request which is an error-control method performed during data transmission. At step 306, RLC PDUs are generated by performing fragmentation or packing functions. At step 307, MAC PDUs are generated by performing multiplexing of RLC PDUs. At step 308, the PHY PDUs are generated from the MAC PDUs and provided to physical carrier 300C.
At the transmitter (i.e. UE in case of uplink and eNB in case of downlink), it is determined whether the IP packets received (packets are received by the eNB from the serving gateway in case of downlink and packets are received from application or IP layer in case of uplink) from the upper layer belongs to which radio bearer. Multiple radio bearer may exists between the UE and eNB to carry different IP flows.
The IP packets (also termed as PDCP service data units (SDUs)) are then mapped to appropriate PDCP unit which applies the header compression and security functions and generates the PDCP PDU. The header compression & security functions are applied by the PDCP layer in the protocol stack. The header compression and security functions are optional and are configurable at the time of radio bearer establishment. The PDCP layer also performs sequence numbering of PDCP SDUs. An instance of PDCP layer or PDCP unit processes the PDCP SDUs. Each EPS bearer is associated with one RB which in turn is associated with one PDCP unit. The generated PDCP PDU (also termed as RLC SDU) is then mapped to appropriate RLC unit which applies the ARQ, fragmentation or packing functions and generates the RLC PDUs. The RLC PDUs (also termed as MAC SDUs) from one or more RBs are then processed by MAC layer unit to generate the MAC PDUs which are then given to physical layer for transmission on physical carrier. There is only one MAC layer unit per UE whereas there is one PDCP and RLC unit per radio bearer. There is one PDCP and RLC unit per EPS bearer as there is one to one mapping between the EPS bearer and radio bearer.
Process Performed at Receiver 300B:
At step 309, the received PHY PDUs are processed to generate MAC PDUs. At step 310, the MAC PDUs are de-multiplexed to generate RLC PDUs. At step 311, the RLC PDUs are processed by performing functions of unpacking and reassembling. At step 312, ARQ function is performed on the received RLC PDUs. At step 313, Security function is performed on PDUs. At step 314, sequence number of PDUs is checked and duplicate PDUs are detected and removed. At step 315, header de-compression is performed on the sequenced PDUs.
At the receiver (i.e. UE in case of downlink and eNB in case of uplink) physical layer receives the packets from the transmitter (UE in case of uplink and eNB in case of downlink) on the physical carrier. The physical layer processes the received packets and sends the received MAC PDUs to the MAC layer. The MAC layer unit de-muxes the RLC PDUs and passes them to appropriate RLC unit. RLC unit applies header parsing, unpacking, reassembly functions and ARQ functions to generate the PDCP PDUs and passes them to appropriate PDCP unit. The PDCP unit then applies the security and header decompression functions and sends the generated packets to IP layer in case the receiver is an UE or serving gateway in case the receiver is an eNB.
One of the ways to support data rate in order of Giga bits is to use multiple processors. One of the challenges in this layered architecture of user plane packet processing is the modularization of MAC and RLC processing into smaller and parallelizable processing units (with minimal sharing of common data) such that they can be efficiently deployable on multi-core processor architectures to achieve very high data rates which are envisaged in 5G & beyond mobile communication systems.